Method of producing a hood, and a hood produced according to the method

ABSTRACT

The disclosure relates to a method of producing a hood for a hearing protector by injection moulding of plastic material. The hood is injection moulded to a single contiguous piece employing at least two plastic materials possessing different properties in at least one respect. The plastic materials may be both homogeneous and in porous or foamed form. A hood for a hearing protector is produced from plastic by injection moulding. The hood includes at least two portions or layers which are united to one another. The portions or layers consist of plastic materials with different properties in at least one respect.

FIELD OF THE INVENTION

The present invention relates to a method of producing a hood for ahearing protector, the hood being produced by injection moulding ofplastic material.

The present invention also relates to a hood for a hearing protector inwhich the hood is produced from plastic by injection moulding.

DESCRIPTION OF THE RELATED ART

A multiplicity of various acoustic hoods are previously known in the artfor use in hearing protectors. Such hoods may be simple and consist of acup-shaped shell injection moulded from plastic which is secured in oneend of an arc which is placed over the head of the wearer and which hasa similar hood at its opposite end. The hoods are dimensioned to enclosethe wearer's ears.

A hood consisting exclusively of a shell is, despite quite complicatedconfiguration, readily subjected to vibrations and oscillations,throughout the entirety of the hood or only locally in it, which impliesthat the sound-suppression or sound insulation which the hoodachieves-will be unpredictable and uneven within various frequencyranges.

In order to obviate the above-mentioned problem, various inlays ofdifferent sound-absorbing materials have been placed interiorly in thehood. Such solutions also suffer from similar drawbacks.

EP 484 306 discloses a hearing protector in which the hoods have a hardouter shell, inside this a casing of compressed foamed plastic, andinside this casing a further hard hood, which realises compression ofthe foamed layer lying outside. Interiorly in the inner hood, asound-absorbent material is then placed.

Such a construction functions considerably better than theabove-described construction consisting merely of a shell which isprovided interiorly with a sound-absorbent. However, the construction isnot optimal, either as regards rational production orsound-suppression/sound-insulation.

Similar constructions are also known from USPS 2 684 067, DE 3 441 120,DE 3 441 122, and others.

For a hood to be as favourable as possible in a hearing protector, thematerial in the hood should be “as dead as possible” so that it has avery slight ability to be excited into oscillation movements both as anentity and also locally.

SUMMARY OF THE INVENTION

The present invention provides a method of manufacturing a hood whichobviates the drawbacks inherent in hoods according to prior arttechnology, and in particular improves the sound-suppression capabilityof the hood. The present invention further provides extremely rationalproduction of hoods, at the same time as these can be given an extremelyaesthetically attractive appearance.

The present invention also obviates the drawbacks inherent in priori artdesigns and constructions, and in particular improves thesound-suppression capability of the hood. Finally, the present inventionprovides a the hood such that it may be manufactured economically andrationally in large series and that it may be given an aestheticallyattractive exterior.

More specifically, the invention provides a hood that is injectionmoulded to one single continuous piece using plastic materials withdifferent properties in at least one respect.

As regards the hood, the objects of the present invention will beattained if the hood is characterised in that it includes at least twomutually contiguous portions or layers which consist of plastic materialwith different properties in at least one respect.

By injection moulding of a hood where different portions are included inthe hood, and where the injection moulded plastic material or materialshave different properties in at least one respect, a hood will berealised which suffers from considerably less of a risk of beingsubjected to resonance oscillations both locally and for the hood as anentity. The hood will have improved sound-suppression capability.

Further, the possibility is afforded of extremely rational manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detailhereinbelow, with particular reference to the accompanying Drawings. Inthe accompanying Drawings:

FIG. 1 is a perspective view of a part of a hearing protector employinga hood according to the present invention;

FIG. 2 is a cross section through a first embodiment of a hood accordingto the present invention; and

FIG. 3 is a partial cross sectional, on a larger scale, of a secondembodiment of a hood according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The basic concept behind the present invention is that there should beincluded, in one and the same hearing protector hood, at least twoportions where the material in each portion differs in one way oranother as regards oscillation from the material in the other portion orin the remaining portions. Differences which will be topical forconsideration here are differences in density, differences in hardness,differences in modulus of elasticity, differences in structure, forexample differences between homogeneous and porous plastic materials,differences between plastic materials with open or closed foamedstructure, differences between plastic materials with and withoutdifferent types of fillers, etc. As examples of usable plastics, mentionmight be made of ABS plastic, polypropylene, polyethylene and polycarbonplastics, TPE, etc.

The concept which lies behind the present invention takes as its pointof departure the fact that a sound wave, i.e. a mechanical oscillationmovement, which propagates in a body will at least partly be reflectedand refracted when it impinges on an interface between materials withdifferent properties. The reflected and refracted parts of the soundwave will interfere with each other and with the original sound wave,with a diffusion and attenuation of the sound wave as a result. Thisphenomenon becomes more manifest the higher the frequency the sound wavehas.

If one considers a body, e.g. a hood included in a hearing protector,its oscillation properties are determined by material properties,configuration and dimensions. Different materials oscillate at differentfrequencies if the remaining properties remain constant. If two bodieswhich oscillate at different frequencies (e.g. depending upon differentmaterial properties in the bodies) are mechanically interconnected, thedifferent oscillations will inhibit one another, whereby resonances areobstructed or reduced.

In FIG. 1, reference numeral 1 relates to a hood included in a hearingprotector, the hood being pivotally secured in a stirrup 2 which isintended to extend over the head of the wearer of the hearing protector.On the side of the hood 1 facing towards the wearer's head, there isprovided an abutment ring 3 which is produced from soft, resilient andyieldable material so that it may form itself according to the head ofthe person wearing the hearing protector, and thereby realise a sealbetween the interior of the hood, round the ear of the wearer and theambient surroundings.

When the word “hood” is employed below and in the appended claims, thisrefers exclusively to the hood proper without loosely inserted dampingmaterial or other equipment and also without the above-mentionedabutment ring.

In the embodiment according to FIG. 2, the hood 1 is produced byinjection moulding in accordance with the sandwich method. The hood 1has a peripheral edge 4 facing towards the wearer's head and along whichthe above-mentioned-abutment ring 3 is secured.

On its outside, the hood 1 has a sprue 5 via which molten plasticmaterial is injected in under high pressure into the mould in which thehood 1 is produced. According to the sandwich method, a first plasticmaterial which is to form the outer casing 6 of the hood and its innercasing 7 is injected in first. When injection of this first plasticmaterial is completed, the injection continues with a second plasticmaterial which is injected interiorly in the material which formed theouter casing and the inner casing. The first and second plasticmaterials have different material properties in at least one respect,such as density, hardness, etc. The second plastic material forms anintermediate layer 8 between the outer casing 6 and the inner casing 7.It should be observed that the outer casing 6 and the inner casing 7have a connecting bridge 9 along the peripheral edge 4 of the hood 1. Asa result, the material in the intermediate layer 8 will in principle betotally enclosed between the outer casing and the inner casing, possiblyapart from the region at the sprue 5.

On injection moulding according to the sandwich method, the plasticmaterial for the outer casing and the inner casing is fed to themoulding tool via a first feeder screw included in the injectionmoulding machine. A second feeder screw is employed for injecting thesecond material for the intermediate layer 8, in which event the toolmay either have two separate inlets, one for each screw, or the tool mayalso be switched from a position for injection via the first screw to aposition for injection via the second screw.

In the embodiment according to FIG. 1, the hood 1 has an outer,peripheral portion 10 which extends along the periphery of the hoodapart from in its upper region. The bottom of the hood, i.e.substantially its central region, and its upper region are formed from acentral portion 11 which is discrete from the outer portion 10 via aseparation line 12 which, in practice, is only visual since the materialin the outer portion 10 and the central portion 11 in principle form asingle, contiguous piece where the different portions have materialswith different properties.

In one variation of the embodiment according to FIG. 1, the outerportion 10 has a through-going material thickness such that the hood 1has the same material externally and internally within the region whichis defined by the outer portion 10. The corresponding feature naturallyapplies to the central portion 11. In another variation of theembodiment according to FIG. 1, the material within the outer portion 10is double, with an outer layer which has a free surface on the outsideof the hood, and an inner layer whose material differs from the materialin the outer layer. The corresponding applies to the central portion 11,but however the materials in the outer and inner layers have beenreversed, so that the material in the outer layer of the outer portionlies on the inside of the central portion 11, while the material in theouter layer within the central portion 11 lies on the inside of theouter layer in the outer portion 10. In the region of the separationline 12, the layers have mutually corresponding apertures and bridges,which will be illustrated more clearly with reference to FIG. 3.

FIG. 3 shows a duplex layer construction where the division between thelayers may have any optionally formed separation lines which can defineconsiderably more different regions than applies in FIG. 1, where onlytwo different regions are shown.

In the embodiment according to FIG. 3, the shell 1 has, in its upperregion in the Figure, a soft inner layer 13 and a hard outer layer 14.The two layers 13 and 14 are united to one another in a union interfacewhere the materials have been caused to adhere powerfully to oneanother, possibly by fusion, during the injection moulding cycle proper.In the lower region of the embodiment according to FIG. 3, the softmaterial is outermost and forms an external band 13′ along theperipheral edge 4 of the hood 1. On the inside of this external band13′, the hard material is located and there forms an inner band 14′.

The transition region between the edge area 16 of the hood 1 and itscupola area 17 includes alternatingly disposed bridges 18 andcomplementary apertures 19 accommodating the bridges 19.

As will be apparent from FIG. 1, an abutment ring 3 extends along theperipheral edge 4 of the hood 1. This has a carrier ring 20 with catches21 or a circumferential ring for snapping into a groove 22 in the insideof the inner, hard band 14′. For the satisfactory function of thehearing protector, it is of vital importance that a good seal isobtained, on the one hand, between the interior of the hood 1 and theabutment ring 3 and, on the other hand, between the abutment ring 3 andthe head of the wearer of the hearing protector. In the embodimentillustrated in FIG. 3, the outer, soft band 13′ has been given the formof a seal 23 which abuts elastically compressed against the upper sideof the carrier ring 20.

The division between the portions 10 and 11 of the hood 1 shown in FIG.1 has been made merely for purposes of exemplification. Aestheticconsiderations may be made in this design, without appreciably affectingthe acoustic properties of the hood. On the other hand, it mightpossibly be expected that a division into more than two differentcontiguous portions may have a favourable effect on the acousticproperties of the hood.

1. A method of producing a hood for a hearing protector, comprising:injection molding of plastic material into a single contiguous pieceemploying plastic materials with different properties in at least onerespect wherein said single contiguous piece includes at least twocontiguous portions, the hood having an outer surface and an innersurface, said at least two contiguous portions being visible on saidouter surface, and wherein one of said at least two contiguous portionscomprises a central portion and another of said at least two contiguousportions at least partially surrounds said central portion.
 2. Themethod as claimed in claim 1, wherein the plastic materials are employedin both homogeneous and in porous or foamed form.
 3. The method asclaimed in claim 1, wherein at least two different plastic materials areemployed.
 4. The method as claimed in claim 3, wherein plastic materialsof different densities are employed.
 5. The method as claimed in claim3, wherein plastic materials of different hardnesses are employed. 6.The method as claimed in claim 3, wherein plastic materials withdifferent modulus of elasticity are employed.
 7. A hood for a hearingprotector produced from plastic by injection molding, comprising: atleast two mutually contiguous portions which comprise plastic materialswith different properties in at least one respect wherein the hood hasan outer surface and an inner surface, said at least two contiguousportions being visible on said outer surface, a separation lineseparating said at least two contiguous portions, and wherein one ofsaid at least two contiguous portions comprises a central portion andanother of said at least two contiguous portions at least partiallysurrounds said central portion.
 8. The hood as claimed in claim 7,wherein at least one portion comprises a different plastic material thananother portion.
 9. The hood as claimed in claim 7, wherein a portion isdisposed along a peripheral edge of the hood, is produced from a softand elastic material, and is designed for sealing against an abutmentring which is disposed along the peripheral edge of the hood anddesigned to abut against a head of a wearer of the hearing protector inwhich the hood is included.
 10. The method as claimed in claim 1 whereinone of said at least two contiguous portions comprises a softer plasticthan the other of said contiguous portions.
 11. The method as claimed inclaim 1 including an abutment ring attached to said hood.
 12. The hoodas claimed in claim 7 wherein one of said at least two contiguousportions comprises a softer plastic than the other of said contiguousportions.
 13. The hood as claimed in claim 7 including an abutment ringattached to said hood.
 14. A hood for a hearing protector comprising: atleast two mutually contiguous portions which comprise plastic materialswith different properties in at least one respect; and wherein the hoodhas an outer surface and an inner surface, said at least two contiguousportions being visible on said outer surface, a separation lineseparating said at least two contiguous portions, and wherein one ofsaid at least two contiguous portions comprises a central portion andanother of said at least two contiguous portions at least partiallysurrounding said central portion.
 15. The hood as claimed in claim 14,wherein at least one portion comprises a different plastic material thananother portion.
 16. The hood as claimed in claim 14, wherein a portionis disposed along a peripheral edge of the hood, is produced from a softand elastic material, and is designed for sealing against an abutmentring which is disposed along the peripheral edge of the hood anddesigned to abut against a head of a wearer of the hearing protector inwhich the hood is included.
 17. The hood as claimed in claim 14 whereinone of said at least two contiguous portions comprises a softer plasticthan the other of said contiguous portions.
 18. The hood as claimed inclaim 14 including an abutment ring attached to said hood.
 19. A methodof producing a hood for a hearing protector, the hood having an outersurface and an inner surface, comprising: injection molding a firstplastic material to form a first portion; injection molding a secondplastic material to form a second portion, said first and secondportions being mutually contiguous to each other to define a singlecontiguous hood, said first and second portions being separated by aseparation line which is visible on said outer surface of said hood,said first portion comprising a central portion and said second portionat least partially surrounding said central portion, said first plasticmaterial having different properties in at least one respect from saidsecond plastic material and wherein one of said first or second plasticmaterials is softer relative to the other of said first or secondplastic materials.
 20. A hood for a hearing protector produced fromplastic injection molding comprising: a first portion formed frominjection molding a first plastic material; a second portion formed frominjection molding a second plastic material; said first and secondportions being mutually contiguous to each other to define a singlecontiguous hood, said first and second portions being separated by aseparation line which is visible on said outer surface of said hood,said first portion comprising a central portion and said second portionat least partially surrounding said central portion, said first plasticmaterial having different properties in at least one respect from saidsecond plastic material and wherein one of said first or second plasticmaterials is softer relative to the other of said first or secondplastic materials.
 21. A hood for a hearing protector comprising: afirst portion formed from a first plastic material; a second portionformed from a second plastic material; said first and second portionsbeing mutually contiguous to each other to define a single contiguoushood, said first and second portions being separated by a separationline which is visible on said outer surface of said hood, said firstportion comprising a central portion and said second portion at leastpartially surrounding said central portion, said first plastic materialhaving different properties in at least one respect from said secondplastic material and wherein one of said first or second plasticmaterials is softer relative to the other of said first or secondplastic materials.
 22. A method of producing a hearing protectorcomprising a hood and an abutment ring, the abutment ring being disposedalong a peripheral edge of the hood, the abutment ring intended to abutagainst the head of a wearer of the hearing protector in which the hoodis included, wherein the hood is produced by a method, comprising:injection molding of plastic material into a single contiguous pieceemploying plastic materials with different properties in at least onerespect.
 23. The method as claimed in claim 22, wherein the plasticmaterials are employed in both homogeneous and in porous or foamed form.24. The method as claimed in claim 22, wherein at least two differentplastic materials are employed.
 25. The method as claimed in claim 24,wherein plastic materials of different densities are employed.
 26. Themethod as claimed in claim 24, wherein plastic materials of differenthardnesses are employed.
 27. The method as claimed in claim 24, whereinplastic materials with different modulus of elasticity are employed. 28.The method as claimed in claim 22 wherein the single contiguous pieceincludes at least two contiguous portions.
 29. The method as claimed inclaim 28 wherein the hood has an outer surface and an inner surface andwherein said at least two contiguous portions are visible on said outersurface.
 30. The method as claimed in claim 29 wherein a separation lineseparates said at least two contiguous portions visible on said outersurface.
 31. The method as claimed in claim 30 wherein one of said atleast two contiguous portions comprise a central portion and another ofsaid at least two contiguous portions at least partially surrounds saidcentral portion.
 32. The method as claimed in claim 30 including two ofsaid contiguous portions wherein one of said portions comprises a softerplastic than the other of said contiguous portions.
 33. A hearingprotector comprising a hood and an abutment ring, the abutment ringbeing disposed along a peripheral edge of the hood, the abutment ringintended to abut against the head of a wearer of the hearing protectorin which the hood is included, wherein the hood is produced from plasticby injection molding, comprising: at least two mutually contiguousportions which comprise first and second plastic made of differentmaterials and with different properties in at least one respect.
 34. Thehearing protector as claimed in claim 33, wherein the portions includean outer and an inner layer of a first plastic material with a firstgroup of properties and an intermediate layer located therebetween andcomprising a second plastic material with a second group of properties.35. The hearing protector as claimed in claim 34, wherein the outer andinner layers have a hardness greater than the intermediate layer. 36.The hearing protector as claimed in claim 35, wherein the intermediatelayer has a hardness greater than the outer and inner layers.
 37. Thehearing protector as claimed in claim 33, wherein the portions includetwo material layers, of which at least one has surfaces which are freetowards both an outside and an inside of the hood.
 38. The hearingprotector as claimed in claim 33, wherein the portions include twomaterial layers which both have surfaces which are free towards anoutside of the hood and surfaces which are free towards the inside ofthe hood.
 39. The hearing protector as claimed in claim 33, wherein atleast one portion comprises a different plastic material than anotherportion.
 40. The hearing protector as claimed in claim 33 wherein acontiguous portion disposed along said peripheral edge of the hood isproduced from a soft and elastic material and is designed for sealingagainst said abutment ring.
 41. The hearing protector as claimed inclaim 35, wherein the intermediate layer has a foam structure.
 42. Thehearing protector as claimed in claim 36, wherein the outer and innerlayers have a foam structure.
 43. The hearing protector as claimed inclaim 33 wherein the hood has an outer surface and an inner surface andwherein said at least two contiguous portions are visible on said outersurface.
 44. The hearing protector as claimed in claim 43 wherein aseparation line separates said at least two contiguous portions visibleon said outer surface.
 45. The hearing protector as claimed in claim 44wherein one of said at least two portions comprise a central portion andanother of said at least two portions at least partially surrounds saidcentral portion.
 46. The hearing protector as claimed in claim 44including two of said contiguous portions wherein one of said portionscomprises a softer plastic than the other of said contiguous portions.47. A hearing protector comprising a hood and an abutment ring, theabutment ring being disposed along a peripheral edge of the hood, theabutment ring intended to abut against the head of a wearer of thehearing protector in which the hood is included, wherein the hoodcomprises: at least two mutually contiguous portions which comprisefirst and second plastic made of different materials and with differentproperties in at least one respect.
 48. The hearing protector as claimedin claim 47, wherein the portions include an outer and an inner layer ofa first plastic material with a first group of properties and anintermediate layer located therebetween and comprising a second plasticmaterial with a second group of properties.
 49. The hearing protector asclaimed in claim 48, wherein the outer and inner layers have a hardnessgreater than the intermediate layer.
 50. The hearing protector asclaimed in claim 48, wherein the intermediate layer has a hardnessgreater than the outer and inner layers.
 51. The hearing protector asclaimed in claim 47, wherein the portions include two material layers,of which at least one has surfaces which are free towards both anoutside and an inside of the hood.
 52. The hearing protector as claimedin claim 47, wherein the portions include two material layers which bothhave surfaces which are free towards an outside of the hood and surfaceswhich are free towards the inside of the hood.
 53. The hearing protectoras claimed in claim 47, wherein at least one portion comprises adifferent plastic material than another portion.
 54. The hearingprotector as claimed in claim 47, wherein a contiguous portion disposedalong said peripheral edge of the hood is produced from a soft andelastic material and is designed for sealing against said abutment. 55.The hearing protector as claimed in claim 49, wherein the intermediatelayer has a foam structure.
 56. The hearing protector as claimed inclaim 50, wherein the outer and inner layers have a foam structure. 57.The hearing protector as claimed in claim 47 wherein the hood has anouter surface and an inner surface and wherein said at least twocontiguous portions are visible on said outer surface.
 58. The hearingprotector as claimed in claim 57 wherein a separation line separatessaid at least two contiguous portions visible on said outer surface. 59.The hearing protector as claimed in claim 58 wherein one of saidportions comprise a central portion and another of said portions atleast partially surrounds said central portion.
 60. The hearingprotector as claimed in claim 58 including two of said contiguousportions wherein one of said portions comprises a softer plastic thanthe other of said contiguous portions.
 61. A method of producing a hoodintended for use with a hearing protector where the hearing protectorcomprises a hood and an abutment ring, the abutment ring intended to bedisposed along a peripheral edge of the hood, wherein the hood isproduced by a method consisting essentially of injection molding ofplastic material into a single contiguous piece employing plasticmaterials with different properties in at least one respect.
 62. Themethod as claimed in claim 61, wherein the plastic materials areemployed in both homogeneous and in porous or foamed form.
 63. Themethod as claimed in claim 61, wherein at least two different plasticmaterials are employed.
 64. The method as claimed in claim 63, whereinplastic materials of different densities are employed.
 65. The method asclaimed in claim 63, wherein plastic materials of different hardnessesare employed.
 66. The method as claimed in claim 63, wherein plasticmaterials with different modulus of elasticity are employed.
 67. Themethod as claimed in claim 61 wherein the single contiguous pieceincludes at least two contiguous portions.
 68. The method as claimed inclaim 67 wherein the hood has an outer surface and an inner surface andwherein said at least two contiguous portions are visible on said outersurface.
 69. The method as claimed in claim 68 wherein a separation lineseparates said at least two contiguous portions visible on said outersurface.
 70. The method as claimed in claim 69 wherein one of said atleast two contiguous portions comprise a central portion and another ofsaid at least two contiguous portions at least partially surrounds saidcentral portion.
 71. The method as claimed in claim 69 including two ofsaid contiguous portions wherein one of said portions comprises a softerplastic than the other of said contiguous portions.
 72. A hood intendedfor use with a hearing protector, the hearing protector comprising ahood and an abutment ring, the abutment ring intended to be disposedalong a peripheral edge of the hood, wherein the hood is produced fromplastic by injection molding, consisting essentially of: at least twomutually contiguous portions which comprise plastic materials withdifferent properties in at least one respect.
 73. The hood as claimed inclaim 72, wherein the portions include an outer and an inner layer of afirst plastic material with a first group of properties and anintermediate layer located therebetween and comprising a second plasticmaterial with a second group of properties.
 74. The hood as claimed inclaim 73, wherein the outer and inner layers have a hardness greaterthan the intermediate layer.
 75. The hood as claimed in claim 74,wherein the intermediate layer has a hardness greater than the outer andinner layers.
 76. The hood as claimed in claim 72, wherein the portionsinclude two material layers, of which at least one has surfaces whichare free towards both an outside and an inside of the hood.
 77. The hoodas claimed in claim 72, wherein the portions include two material layerswhich both have surfaces which are free towards an outside of the hoodand surfaces which are free towards the inside of the hood.
 78. The hoodas claimed in claim 72, wherein at least one portion comprises adifferent plastic material than another portion.
 79. The hood as claimedin claim 72 wherein a contiguous portion disposed along said peripheraledge of the hood is produced from a soft and elastic material and isdesigned for sealing against said abutment ring.
 80. The hood as claimedin claim 74, wherein the intermediate layer has a foam structure. 81.The hood as claimed in claim 75, wherein the outer and inner layers havea foam structure.
 82. The hood as claimed in claim 72 wherein the hoodhas an outer surface and an inner surface and wherein said at least twocontiguous portions are visible on said outer surface.
 83. The hood asclaimed in claim 82 wherein a separation line separates said at leasttwo contiguous portions visible on said outer surface.
 84. The hood asclaimed in claim 83 wherein one of said at least two portions comprise acentral portion and another of said at least two portions at leastpartially surrounds said central portion.
 85. The hood as claimed inclaim 83 including two of said contiguous portions wherein one of saidportions comprises a softer plastic than the other of said contiguousportions.
 86. A hood intended for use with a hearing protector, thehearing protector comprising a hood and an abutment ring, the abutmentring intended to be disposed along a peripheral edge of the hood,wherein the hood consists essentially of: at least two mutuallycontiguous portions which comprise plastic materials with differentproperties in at least one respect.
 87. The hood as claimed in claim 86,wherein the portions include an outer and an inner layer of a firstplastic material with a first group of properties and an intermediatelayer located therebetween and comprising a second plastic material witha second group of properties.
 88. The hood as claimed in claim 87,wherein the outer and inner layers have a hardness greater than theintermediate layer.
 89. The hood as claimed in claim 87, wherein theintermediate layer has a hardness greater than the outer and innerlayers.
 90. The hood as claimed in claim 86, wherein the portionsinclude two material layers, of which at least one has surfaces whichare free towards both an outside and an inside of the hood.
 91. The hoodas claimed in claim 86, wherein the portions include two material layerswhich both have surfaces which are free towards an outside of the hoodand surfaces which are free towards the inside of the hood.
 92. The hoodas claimed in claim 86, wherein at least one portion comprises adifferent plastic material than another portion.
 93. The hood as claimedin claim 86, wherein a contiguous portion disposed along said peripheraledge of the hood is produced from a soft and elastic material and isdesigned for sealing against said abutment.
 94. The hood as claimed inclaim 88, wherein the intermediate layer has a foam structure.
 95. Thehood as claimed in claim 89, wherein the outer and inner layers have afoam structure.
 96. The hood as claimed in claim 86 wherein the hood hasan outer surface and an inner surface and wherein said at least twocontiguous portions are visible on said outer surface.
 97. The hood asclaimed in claim 96 wherein a separation line separates said at leasttwo contiguous portions visible on said outer surface.
 98. The hood asclaimed in claim 97 wherein one of said portions comprise a centralportion and another of said portions at least partially surrounds saidcentral portion.
 99. The hood as claimed in claim 97 including two ofsaid contiguous portions wherein one of said portions comprises a softerplastic than the other of said contiguous portions.
 100. A method ofproducing a hood for a hearing protector, comprising: injection moldingthe hood from plastic materials to form a single piece having at leasttwo contiguous portions, the plastic materials adhering to one anotherduring the inject molding process, the plastic materials havingdifferent properties in at least one respect so as to improve the soundsuppression capability of the hood by sound wave interference at aninterface between the at least two contiguous portions.
 101. The methodas claimed in claim 100 wherein the plastic materials are employed inboth homogeneous and in porous or foamed form.
 102. The method asclaimed in claim 100 wherein at least two different plastic materialsare employed.
 103. The method as claimed in claim 102 wherein plasticmaterials of different densities are employed.
 104. The method asclaimed in claim 102 wherein plastic materials of different hardnessesare employed.
 105. The method as claimed in claim 102 wherein plasticmaterials with different modulus of elasticity are employed.
 106. A hoodfor a hearing protector, the hood being produced from plastic byinjection molding, wherein the hood includes at least two mutuallycontiguous portions or layers which consist of plastic materials, theplastic materials adhering to one another during the injection moldingcycle, with the plastic materials having different properties in atleast one respect so as to improve the sound-suppression capability ofthe hood by sound wave interference at an interface between thecontiguous portions or layers.
 107. The hood as claimed in claim 106wherein the portions include an outer and an inner layer of a plasticmaterial with a first group of properties and an intermediate layerlocated therebetween, the intermediate layer comprising a plasticmaterial with a second group of properties.
 108. The hood as claimed inclaim 107 wherein the outer and inner layers are relatively hard, whilethe intermediate layer is softer or has a foamed structure.
 109. Thehood as claimed in claim 107 wherein the intermediate layer isrelatively hard while the outer and inner layers are softer or have afoamed structure.
 110. The hood as claimed in claim 106 wherein theportions include two material layers, of which at least one has surfaceswhich are exposed to both the outside of the hood and to the inside ofthe hood.
 111. The hood as claimed in claim 106 wherein the portionsinclude two material layers which both have surfaces which are exposedto the outside of the hood and surfaces which are exposed to the insideof the hood.
 112. The hood as claimed in claim 106 wherein at least oneof the portions or layers comprised a different plastic material thanthe other portion or layers.
 113. The hood as claimed in claim 106wherein a portion is disposed along the peripheral edge of the hood,wherein such portion is produced from a soft and elastic material and isintended to seal against an abutment ring which is disposed along aperipheral edge of the hood, the abutment ring intended to abut againstthe head of the wearer of the hearing protector in which the hood isincluded.